GTP-binding proteins often play critical roles in cellular metabolism. Three GTP-binding regulatory proteins are termed Gs, Gi, and transducin which mediate hormonal stimulation of adenylate cyclase, hormonal inhibition of adenylate cyclase, and light activation of the phosphodiesterase of retinal rod outer segments, respectively. All three proteins exhibit striking structural and functional homologies. In order to define the molecular mechanisms by which these proteins mediate hormonal or light-controlled processes, we have begun to clone the genes coding for these proteins. Since transducin can be isolated in larger quantities than Gs or Gi, initial studies were directed towards purifying transducin subunits. After isolation of transducin and separation of its three subunits (termed Alpha, Beta, and Gamma), sequence data from each of the subunits were obtained. Oligonucleotide probes were synthesized based on these sequences. In addition, polyclonal and monoclonal antibodies to holotransducin and its subunits were prepared to use as additional probes for the transducin genes. These antibodies were found to interfere with transducin enzymatic activity. Moreover, antitransducin BetaGamma antibodies cross-reacted with the corresponding adenylate cyclase components.